As already known and described in detail in numerous patent documents, spinning-rotors of open-end-spinning devices generally have a rotor shaft for bearing and driving the spinning rotor and a rotor cup arranged on the rotor shaft for producing a yarn.
In open-end spinning devices which operate at high speeds, of for example greater than 130 000 rpm, the spinning rotors are increasingly equipped with a single drive and mounted magnetically for example.
In such spinning rotors driven with single motors also the rotor shaft is generally designed in two parts, that is the rotor shaft consists of a front part to which the rotor cup is fixed, and a rear part which comprises the rotor-side components of the drive and the magnetic bearing of the spinning rotor.
The two rotor shaft parts are connected to one another during the spinning operation by a coupling device and can be detached from one another if necessary.
As such spinning rotors have to be accelerated again to their operating speed after each interruption in the spinning and the operating speeds of such modern open-end rotor spinning machines, as indicated above, can be greater than 150.000 rpm, it is advantageous if the rotating parts of an open-end rotor spinning device have the lowest possible inertia moment, that is if the spinning rotors are built to be as light as possible.
The high operating speeds of modern open-end rotor spinning machines thus make very high demands on the spinning rotors, both with regard to the radial run-out and bearing which also relates to their speed performance.
In German Patent Publication DE 199 10 277 B4 spinning rotors are described which are used in modern open-end-rotor spinning machines and are designed accordingly for high operating speeds.
Said known spinning rotors comprise rotor cups, which are rotated respectively from a solid material and have an aerodynamically advantageously designed outer surface. The rotor cups of said spinning rotors have an annular wall section, which is designed so that the thickness of the wall section continually increases slightly from the opening of the rotor cup in the direction of the rotor bottom.
The rotor bottom of said spinning rotors is also designed so that the cross-section of the rotor bottom increases from the outside inwardly. This means that such spinning rotors have their greatest thickness in the region of the central connecting collar, in which the front part of the rotor shaft is mounted.
In practice such spinning rotors are also characterized by being highly effective, however at very high speeds of the spinning rotors due to the centrifugal forces occurring in the region of the rotor cups often large material stresses are produced.
Spinning rotors, which can be operated at very high operating speeds and are characterized by high efficiency, are also known from German Patent Publications DE 10 2005 021 920 A1 and DE 10 2007 007 260 A1.
In said literature different joining methods are described by means of which in a spinning rotor, which is driven by a single motor and is mounted magnetically, the rotor cup can be connected reliably to an associated rotor shaft part.
The rotor cups of said spinning rotors are characterized by having a weight-optimised structure, wherein the rotor shaft is designed in two parts.
This means that in these known spinning rotors a first rotor shaft part comprises the rotor side components of the spinning rotor drive and the spinning rotor bearing, whereas the rotor cup is secured on a second rotor shaft part, which if necessary is mounted exchangeably in the first rotor shaft part.
According to German Patent Publication DE 10 2005 021 920 A1 for example the front part of the rotor shaft and the relatively thin-walled rotor cup comprise connecting means which are at least partly cast around by a connecting element designed as a casting. In the cooled state the casting then forms a form-fitting connection between the front rotor shaft part and the rotor cup.
In German Patent Publication DE 10 2007 007 260 A1 a joining method is described in which the thin-walled rotor cup of a spinning rotor can be connected by an adhesive bond directly or indirectly in a rotationally secure manner to a front rotor shaft part.
By means of such an adhesive bond in a relatively simple manner a significant reduction in mass is achieved compared to previously conventional types of connection, with the result that spinning rotors produced in this way are relatively light and can thus be accelerated and braked effectively.
The reduction of the mass inertia moment of the spinning rotor achieved by using an adhesive bond according to the invention not only has a positive effect on the acceleration behaviour of the spinning rotor, but the reduction in weight of the spinning rotors also leads to a reduction in the power consumption which in a textile machine with a plurality of workstations results in a noticeable saving for each machine.
As indicated above, in such spinning rotors, in particular at very high speeds, the material of the rotor cups is subjected to high material stresses.
In order to prevent the overloading of the rotor cup material with occurring centrifugal forces, therefore in practice the speeds, at which such spinning rotors can be operated, are limited for example to 150 000 rpm.
By means of European Patent Publication EP 0 154 358 A2 spinning rotors are also known the rotor cups of which are produced by non-cutting shaping. In these known spinning rotors a cold-rolled fine steel sheet is used as a starting material for the rotor cup, which is shaped by means of suitable tools into a rotor cup.
As in such rotor cups produced by non-cutting shaping there is a risk that because of the high speeds of the spinning rotors high centrifugal forces may lead to deformations of the rotor cups, the rotor cups of such spinning rotors also have a reinforcement in the region of the rotor cup opening.
The reinforcement is thus either designed as a flange arranged in the region of the rotor cup opening, or as a ring, which in the region of the rotor cup opening is fitted onto the outer circumference of the rotor cup.
Also in said spinning rotors, to prevent overloading of the rotor cup material by the centrifugal forces produced, the speeds at which such spinning rotors can be operated are limited.